Plane-parallel structures of silicon/silicon oxide

ABSTRACT

The present invention relates to plane-parallel structures of silicon/silicon oxide (silicon/silicon oxide flakes), obtainable by heating plane-parallel structures of SiO y  in an oxygen-free atmosphere at a temperature above 400° C., wherein 0.70≦y≦1.8, or plane-parallel structures of silicon/silicon oxide, obtainable by heating plane-parallel structures of SiO x  in an oxygen-free atmosphere at a temperature above 400° C., wherein 0.03≦x≦0.95, a process for their production and their use for the production of interference pigments.

The present invention relates to plane-parallel structures ofsilicon/silicon oxide (silicon/silicon oxide flakes), obtainable byheating plane-parallel structures of SiO_(y) in an oxygen-freeatmosphere at a temperature above 400° C., wherein 0.70≦y≦1.8, orplane-parallel structures of silicon/silicon oxide, obtainable byheating plane-parallel structures of SiO_(x) in an oxygen-freeatmosphere at a temperature above 400° C., wherein 0.03≦x≦0.95, aprocess for their production and their use for the production ofinterference pigments.

In a first aspect the present invention relates to plane-parallelstructures of silicon/silicon oxide.

The particles of the plane-parallel structures of silicon/silicon oxidegenerally have a length of from 1 μm to 5 mm, a width of from 1 μm to 2mm, and a thickness of from 20 nm to 2 μm, and a ratio of length tothickness of at least 2:1, the silicon/silicon oxide particles havingtwo substantially parallel faces, the distance between which is theshortest axis of the core.

The flakes of the present invention are not of a uniform shape.Nevertheless, for purposes of brevity, the flakes will be referred to ashaving a “diameter.” The silicon/silicon oxide flakes have a highplane-parallelism and a defined thickness in the range of ±10%,especially ±5% of the average thickness. The silicon/silicon oxideflakes have a thickness of from 20 to 2000 nm, especially from 100 to350 nm. It is presently preferred that the diameter of the flakes be ina preferred range of about 1-60 μm with a more preferred range of about5-40 μm. Thus, the aspect ratio of the flakes of the present inventionis in a preferred range of about 2.5 to 625 with a more preferred rangeof about 50 to 250.

The term “SiO_(y) with 0.70≦y≦1.80” means that the molar ratio of oxygento silicon at the average value of the silicon oxide layer is from 0.70to 1.80. The composition of the silicon oxide layer can be determined byESCA (electron spectroscopy for chemical analysis).

The term “SiO_(x) with 0.03≦x≦0.95” means that the molar ratio of oxygento silicon at the average value of the silicon oxide layer is from 0.03to 0.95. The composition of the silicon oxide layer can be determined byESCA (electron spectroscopy for chemical analysis).

The term “silicon/silicon oxide layer or flakes” comprisesplane-parallel structures obtainable by heating plane-parallelstructures of SiO_(y) or SiO_(x) in an oxygen-free atmosphere at atemperature above 400° C. and optionally an oxidative heat treatment.

According to the present invention the term “aluminum” comprisesaluminum and alloys of aluminum. Alloys of aluminum are, for exampledescribed in G. Wassermann in Ullmanns Enzyklopädie der IndustriellenChemie, 4. Auflage, Verlag Chemie, Weinheim, Band 7, S. 281 to 292.Especially suitable are the corrosion stable aluminum alloys describedon page 10 to 12 of WO00/12634, which comprise besides of aluminumsilicon, magnesium, manganese, copper, zinc, nickel, vanadium, lead,antimony, tin, cadmium, bismuth, titanium, Chromium and/or iron inamounts of less than 20% by weight, preferably less than 10% by weight.

The present invention is illustrated in more detail on the basis of the“SiO_(y) flakes”, but is not limited thereto.

The silicon/silicon oxide flakes are prepared by a process comprisingthe steps:

-   a) vapour-deposition of a separating agent onto a (movable) carrier    to produce a separating agent layer,-   b) vapour-deposition of an SiO_(y) layer onto the separating agent    layer, wherein 0.70≦y≦1.8, preferably wherein 0.70≦y≦0.99 or    1.0≦y≦1.8,-   c) dissolution of the separating agent layer in a solvent,-   d) separation of the SiO_(y) from the solvent, and-   e) heating the SiO_(y) in an oxygen-free atmosphere to a temperature    above 400° C.

The SiO_(y) layer in step b) being vapour-deposited from a vaporisercontaining a charge comprising a mixture of Si and SiO₂, SiO_(y) or amixture thereof, the weight ratio of Si to SiO₂ being preferably in therange from 0.15:1 to 0.75:1, and especially containing a stoichiometricmixture of Si and SiO₂ or a vaporiser containing a charge comprisingsilicon monoxide containing silicon in an amount up to 20% by weight.Step c) being advantageously carried out at a pressure that is higherthan the pressure in steps a) and b) and lower than atmosphericpressure. The SiO_(y) flakes obtainable by this method have a thicknessin the range preferably from 20 to 2000 nm, especially from 20 to 500nm, the ratio of the thickness to the surface area of the plane-parallelstructures being preferably less than 0.01 μm⁻¹. The plane-parallelstructures thereby produced are distinguished by high uniformity ofthickness the SiO_(1.00-1.8) layer in step b) is formed preferably fromsilicon monoxide vapour produced in the vaporiser by reaction of amixture of Si and SiO₂ at temperatures of more than 1300° C.

The SiO_(0.70-0.99) layer in step b) is formed preferably by evaporatingsilicon monoxide containing silicon in an amount up to 20% by weight attemperatures of more than 1300° C.

If, under industrial vacuums of a few 10⁻² Pa, Si is vaporised (insteadof Si/SiO₂ or SiO/Si) silicon oxides can be obtained which have anoxygen content of less than 0.95, that is to say SiO_(x), wherein0.03≦x≦0.95, especially 0.05≦x≦0.50, very especially 0.10≦x≦0.30(PCT/EP03/02196).

The vapour-deposition in steps a) and b) is carried out preferably undera vacuum of <0.5 Pa. The dissolution of the separating agent layer instep c) is carried out at a pressure in the range preferably from 1 to5×10⁴ Pa, especially from 600 to 10⁴ Pa, and more especially from 10³ to5×10³ Pa.

The separating agent vapour-deposited onto the carrier in step a) may bea lacquer (surface coating), a polymer, such as, for example, the(thermoplastic) polymers, in particular acryl- or styrene polymers ormixtures thereof, as described in U.S. Pat. No. 6,398,999, an organicsubstance soluble in organic solvents or water and vaporisable in vacuo,such as anthracene, anthraquinone, acetamidophenol, acetylsalicylicacid, camphoric anhydride, benzimidazole, benzene-1,2,4-tricarboxylicacid, biphenyl-2,2-dicarboxylic acid, bis(4-hydroxyphenyl)sulfone,dihydroxyanthraquinone, hydantoin, 3-hydroxybenzoic acid,8-hydroxyquinoline-5-sulfonic acid monohydrate, 4-hydroxycoumarin,7-hydroxycoumarin, 3-hydroxynaphthalene-2-carboxylic acid, isophthalicacid, 4,4-methylene-bis-3-hydroxynaphthalene-2-carboxylic acid,naphthalene-1,8-dicarboxylic anhydride, phthalimide and its potassiumsalt, phenolphthalein, phenothiazine, saccharin and its salts,tetraphenylmethane, triphenylene, triphenylmethanol or a mixture of atleast two of those substances. The separating agent is preferably aninorganic salt soluble in water and vaporisable in vacuo (see, forexample, DE 198 44 357), such as sodium chloride, potassium chloride,lithium chloride, sodium fluoride, potassium fluoride, lithium fluoride,calcium fluoride, sodium aluminium fluoride and disodium tetraborate.

The movable carrier may consist of one or more discs, cylinders or otherrotationally symmetrical bodies, which rotate about an axis (cf.WO01/25500), and consists preferably of one or more continuous metalbelts with or without a polymeric coating or of one or more polyimide orpolyethylene terephthalate belts (DE19844357).

Step d) may comprise washing-out and subsequent filtration,sedimentation, centrifugation, decanting and/or evaporation. Theplane-parallel structures of SiO_(y) may, however, also be frozentogether with the solvent in step d) and subsequently subjected to aprocess of freeze-drying, whereupon the solvent is separated off as aresult of sublimation below the triple point and the dry SiO_(y) remainsbehind in the form of individual plane-parallel structures.

The plane-parallel structures of SiO_(y) separated off in step d) arethen heated in an oxygen-free atmosphere such as, for example, argonand/or helium or under a vacuum of less than 13 Pa (10⁻¹ Torr) at atemperature of at least 400° C., especially at above 400° C., preferablyin the form of loose material, in a fluidised bed, preferably at atemperature in the range from 900 to 1100° C., to form thesilicon/silicon oxide flakes.

The invention relates also to plane-parallel structures ofsilicon/silicon oxide that are obtainable by this method and have athickness preferably in the range from 20 to 2000 nm, especially 20 to500 nm.

Except under an ultra-high vacuum, in technical vacuums of a few 10⁻² Pavaporised SiO always condenses as SiO_(y) wherein 1≦y≦1.8, especiallywherein 1.1<y<1.8, because high-vacuum apparatuses always contain, as aresult of gas emission from surfaces, traces of water vapour which reactwith the readily reactive SiO at vaporisation temperature.

On its further course, the belt-form carrier, which is closed to form aloop, runs through dynamic vacuum lock chambers of known mode ofconstruction (cf. U.S. Pat. No. 6,270,840) into a region of from 1 to5×10⁴ Pa pressure, preferably from 600 to 10⁴ Pa pressure, andespecially from 10³ to 5×10³ Pa pressure, where it is immersed in adissolution bath. The temperature of the solvent should be so selectedthat its vapour pressure is in the indicated pressure range. Withmechanical assistance, the separating agent layer rapidly dissolves andthe product layer breaks up into flakes, which are then present in thesolvent in the form of a suspension. On its further course, the belt isdried and freed from any contaminants still adhering to it. It runsthrough a second group of dynamic vacuum lock chambers back into thevaporisation chamber, where the process of coating with separating agentand product layer of SiO is repeated.

The suspension then present in both cases, comprising product structuresand solvent, and the separating agent dissolved therein, is thenseparated in a further operation in accordance with a known technique.For that purpose, the product structures are first concentrated in theliquid and rinsed several times with fresh solvent in order to wash outthe dissolved separating agent The product, in the form of a solid thatis still wet, is then separated off by filtration, sedimentation,centrifugation, decanting or evaporation.

The product can then be brought to the desired particle size by means ofgrinding or air-sieving and delivered for further use.

In the production of the silicon/silicon oxide flakes, variants arepossible:

It is possible to arrange several separating agent and productvaporisers one after the other in the running direction of the belt inthe vaporisation zone. By that means there is obtained, with littleadditional outlay in terms of apparatus, a layer sequence of S+P+S+P,wherein S is the separating agent layer and P is the product layer. Ifthe number of vaporisers is doubled and the belt speed is the same,twice the amount of product is obtained.

Separating off the plane-parallel structures after washing-out atatmospheric pressure can be carried out under gentle conditions byfreezing the suspension, which has been concentrated to a solids contentof about 50%, and subjecting it in known manner to freeze-drying atabout −10° C. and 50 Pa pressure. The dry substance remains behind asproduct, which can be subjected to the steps of further processing bymeans of coating or chemical conversion.

Instead of using a continuous belt, it is possible to produce theproduct by carrying out the steps of vapour-deposition of separatingagent and SiO, of dissolution, and of drying the carrier, in anapparatus having a rotary body, in accordance with WO01/25500. Therotary body may be one or more discs, a cylinder or any otherrotationally symmetrical body.

It should be noted that the silicon/silicon oxide flakes themselves showno colors when embedded in a transparent resin, which has an index ofrefraction ranging from 1.4 to 1.55. In such a case the embeddedsemi-transparent flakes act as UV absorber.

It is assumed that by heating SiO_(y) particles (or SiO_(x) particles)in an oxygen-free atmosphere, i.e. an argon or helium atmosphere or in avacuum of less than 13 Pa (10⁻¹ Torr), at a temperature above 400° C.,especially 400 to 1100° C., SiO_(y) disproportionates in SiO₂ and Si.SiO_(y)→(y/y+a)SiO_(y+a)+(1−(y/y+a))Si

In this disproportion SiO_(y+a) flakes are formed, containing(1−(y/y+a)) Si, wherein 0.70≦y≦1.8, especially 0.70≦y≦0.99 or 1≦y≦1.8,0.05≦a≦1.30, and the sum y and a is equal or less than 2. SiO_(y+a), isan oxygen enriched silicon suboxide. The complete conversion of SiO_(y)in Si and SiO₂ is preferred:SiO_(y)→(y/2)SiO₂+(1−(y/2))Si

In the temperature range of from 400 to 900° C. the formed silicon isamorph. In the temperature range of from 900 to 1100° C. siliconcrystallites are formed. The average crystallite size is in the range offrom 1 to 20 nm, especially 2 to 10 nm. The size is on the one handdependent on the temperature. That is, at 1100° C. larger crystallitesthan at 900° C. are formed. On the other hand a clear tendency for theformation of smaller crystallites is found, the higher the oxygen levelof the SiO_(y) is. Depending on the preparation the Si containing,plane-parallel SiO_(y+a) particles, especially SiO₂ particles can showphotoluminescence. For example, plane-parallel structures of SiO_(0.86)(see example 2), which have been heated in vacuo at 900° C. for at least1 hour, show photoluminescence at a wavelength greater than 800 nm,especially greater than 840 nm (excitation wavelength: ˜300 nm).

Before the silicon/silicon oxide flakes are processed to interferencepigments, they can be subjected to oxidative heat treatment. Knownmethods are available for that purpose. Air or some otheroxygen-containing gas is passed through the silicon/silicon oxideflakes, which are in the form of loose material or in a fluidised bed,at a temperature of more than 200° C., preferably more than 400° C. andespecially from 500 to 1000° C. for several hours.

In order to achieve orientation of the plane-parallel structures ofsilicon/silicon oxide approximately parallel to the surface of thesurface coating layer(s), the surface tension of the structures can bemodified by adding known chemicals to the surface coating, for exampleby means of commercially available silane oligomers. Such oligomers,known under the trade names DYNASILAN™, HYDROSIL™, PROTECTOSIL™ can alsobe deposited directly onto the surface of the plane-parallel structures,either from a liquid phase or by condensation, before the latter areintroduced into the surface coating.

In contrast to silicon oxide flakes, which are white to slightlyyellowish, SiO_(y) flakes, which have been heated at 900° C. under avacuum of less than 10⁻¹ Torr for about one hour (silicon/silicon oxideflakes), become colored in air and are semi-transparent. The observedcolor depends on the thickness of the flakes and changes in dependenceof the observation angle. For particular applications such as cosmeticsthe silicon/silicon oxide flakes can be used as such, whereas for paintapplications the silicon/silicon oxide flakes have to be provided withfurther layers, such as, for example, one or more metal oxide and/ormetal layers, wherein in case of the metal oxide a metal oxide layerhaving a high index of refraction is advantageously deposited first. Itbeing possible, where appropriate, for the metal oxides to be reduced(DE-A-19502231, WO97/39065, DE-A-19843014 and WO00/17277).

Accordingly, the present invention also relates to plane-parallelpigments, comprising a silicon/silicon oxide layer obtainable by heatinga SiO_(y) layer in an oxygen-free atmosphere at a temperature above 400°C., wherein 0.70≦y≦1.8, especially plane-parallel pigments, comprising

-   (a) a silicon/silicon oxide substrate layer obtainable by heating a    SiO_(y) layer in an oxygen-free atmosphere at a temperature above    400° C., wherein 0.70≦y≦1.8,-   (b) a metal oxide of high index of refraction and-   (c) optionally on top of the metal oxide of high index of refraction    a metal oxide of low index of refraction; or to-   plane-parallel pigments, comprising a silicon/silicon oxide layer,    obtainable by heating plane-parallel structures of SiO_(x) in an    oxygen-free atmosphere at a temperature above 400° C., wherein    0.03≦x≦0.95, especially 0.05≦x≦0.50, very especially 0.10≦x≦0.30, or    to plane-parallel pigments, comprising-   (a) a silicon/silicon oxide substrate layer obtainable by heating a    SiO_(y) layer in an oxygen-free atmosphere at a temperature above    400° C., wherein 0.70≦y≦1.8, a semi-transparent metal layer.

Various coating processes can be utilized in forming coating layers.Suitable methods for forming the coating layer include vacuum vapordeposition, sol-gel hydrolysis, CVD in a fluidized bed (U.S. Pat. No.5,364,467 and U.S. Pat. No. 5,763,086), and electrochemical deposition.Another depositing method is the plasma enhanced chemical vapordeposition (PECVD) where the chemical species are activated by a plasma.Such a method is disclosed in detail in WO02/31058.

In principle, the plane parallel pigments can comprise in addition tothe silicon/silicon oxide layer materials having a “low” index ofrefraction, which is defined herein as an index of refraction of about1.65 or less, or can have a “high” index of refraction, which is definedherein as an index of refraction of greater than about 1.65. Various(dielectric) materials that can be utilized include inorganic materialssuch as metal oxides, metal fluorides, metal sulfides, metal nitrides,metal carbides, combinations thereof, and the like, as well as organicdielectric materials. These materials are readily available and easilyapplied by physical or chemical vapor deposition processes.

Nonlimiting examples of suitable low index dielectric materials that canbe used include silicon dioxide (SiO₂), aluminum oxide (Al₂O₃), andmetal fluorides such as magnesium fluoride (MgF₂), aluminum fluoride(AlF₃), cerium fluoride (CeF₃), lanthanum fluoride (LaF₃), sodiumaluminum fluorides (e.g., Na₃AlF₆ or Na₅Al₃F₁₄), neodymium fluoride(NdF₃), samarium fluoride (SmF₃), barium fluoride (BaF₂), calciumfluoride (CaF₂), lithium fluoride (LiF), combinations thereof, or anyother low index material having an index of refraction of about 1.65 orless. For example, organic monomers and polymers can be utilized as lowindex materials, including dienes or alkenes such as acrylates (e.g.,methacrylate), polymers of perfluoroalkenes, polytetrafluoroethylene(TEFLON), polymers of fluorinated ethylene propylene (FEP), parylene,p-xylene, combinations thereof, and the like. Additionally, theforegoing materials include evaporated, condensed and cross-linkedtransparent acrylate layers, which may be deposited by methods describedin U.S. Pat. No. 5,877,895, the disclosure of which is incorporatedherein by reference. Nonlimiting examples of suitable high indexdielectric materials are given below.

Suitable metals for the semi-transparent metal layer are, for example,Cr, Ti, Mo, W, Al, Cu, Ag, Au, or Ni. Preferred pigments have thefollowing layer structure: silicon/silicon oxide+metal+SiO₂+metal oxidehaving a high index of refraction.

In an especially preferred embodiment, the pigment on the basis of thesilicon/silicon oxide substrate, obtainable by heating a SiO_(y) layerin an oxygen-free atmosphere at a temperature above 400° C., wherein0.70≦y≦1.8, comprises a further layer of a dielectric material having a“high” refractive index, that is to say a refractive index greater thanabout 1.65, preferably greater than about 2.0, most preferred greaterthan about 2.2, which is applied to the entire surface of thesilicon/silicon oxide substrate. Examples of such a dielectric materialare zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide (ZrO₂),titanium dioxide (TiO₂), carbon, indium oxide (In₂O₃), indium tin oxide(ITO), tantalum pentoxide (Ta₂O₅), chromium oxide (Cr₂O₃), cerium oxide(CeO₂), yttrium oxide (y₂O₃), europium oxide (EU₂O₃), iron oxides suchas iron(II)/iron(III) oxide (Fe₃O₄) and iron(III) oxide (Fe₂O₃), hafniumnitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO₂), lanthanumoxide (La₂O₃), magnesium oxide (MgO), neodymium oxide (Nd₂O₃),praseodymium oxide (Pr₆O₁₁), samarium oxide (Sm₂O₃), antimony trioxide(Sb₂O₃), silicon monoxides (SiO), selenium trioxide (Se₂O₃), tin oxide(SnO₂), tungsten trioxide (WO₃) or combinations thereof. The dielectricmaterial is preferably a metal oxide, it being possible for the metaloxide to be a single oxide or a mixture of oxides, with or withoutabsorbing properties, for example TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃ orZnO, with TiO₂ being especially preferred.

In this embodiment the thickness of the silicon/silicon oxide substrateis generally from 20 to 1000 nm, preferably from 50 to 500 nm, and thatof the TiO₂ layer generally from 1 to 100 nm, preferably from 5 to 50nm.

It is possible to obtain pigments that are more intense in colour andmore transparent by applying, on top of the TiO₂ layer, a metal oxide oflow refractive index, such as SiO₂, Al₂O₃, AlOOH, B₂O₃ or a mixturethereof, preferably SiO₂, and applying a further TiO₂ layer on top ofthe latter layer (EP-A-892832, EP-A-753545, WO93/08237, WO98/53011,WO9812266, WO9838254, WO99/20695, WO00/42111, and EP-A-1213330).

Additional coatings may be applied in a manner known per se for thepurpose of stabilisation with respect to weather and light.

Pigments on the basis of silicon/silicon oxide substrates, comprising ametal oxide of high index of refraction and optionally on top of themetal oxide of high index of refraction a metal oxide of low index ofrefraction, or a semi-transparent metal layer are preferred.

Pigments on the basis of silicon/silicon oxide substrates, which havebeen coated by a wet chemical method, in the indicated order areparticularly preferred: TiO₂ (substrate: silicon/silicon oxide; layer:TiO₂), (SnO₂)TiO₂, Fe₂O₃, Fe₂O₃.TiO₂ (substrate: silicon/silicon oxide;mixed layer of Fe₂O₃ and TiO₂), TiO/Fe₂O₃ (substrate: silicon/siliconoxide; first layer: TiO₂; second layer: Fe₂O₃), TiO₂/Berlin blau,TiO₂₁Cr₂O₃, TiO₂₁FeTiO₃, TiO₂₁SiO₂/TiO₂, (SnO₂)TiO₂/SiO₂/TiO₂,TiO₂₁SiO₂/TiO₂/SiO₂/TiO₂ or TiO₂/SiO₂/Fe₂O₃.

The metal oxide layers can be applied by CVD (chemical vapourdeposition) or by wet chemical coating. The metal oxide layers can beobtained by decomposition of metal carbonyls in the presence of watervapour (relatively low molecular weight metal oxides such as magnetite)or in the presence of oxygen and, where appropriate, water vapour (e.g.nickel oxide and cobalt oxide). The metal oxide layers are especiallyapplied by means of oxidative gaseous phase decomposition of metalcarbonyls (e.g. iron pentacarbonyl, chromium hexacarbonyl; EP-A45 851),by means of hydrolytic gaseous phase decomposition of metal alcoholates(e.g. titanium and zirconium tetra-n- and -iso-propanolate; DE-A-41 40900) or of metal halides (e.g. titanium tetrachloride; EP-A-338 428), bymeans of oxidative decomposition of organyl tin compounds (especiallyalkyl tin compounds such as tetrabutyltin and tetramethyltin; DE-A-44 03678) or by means of the gaseous phase hydrolysis of organyl siliconcompounds (especially di-tert-butoxyacetoxysilane) described in EP-A-668329, it being possible for the coating operation to be carried out in afluidised-bed reactor (EP-A-045 851 and EP-A-1 06 235). Al₂O₃ layers (B)can advantageously be obtained by controlled oxidation during thecooling of aluminium-coated pigments, which is otherwise carried outunder inert gas (DE-A-195 16 181).

Phosphate-, chromate- and/or vanadate-containing and also phosphate- andSiO₂-containing metal oxide layers can be applied in accordance with thepassivation methods described in DE-A-42 36 332 and in EP-A-678 561 bymeans of hydrolytic or oxidative gaseous phase decomposition ofoxide-halides of the metals (e.g. CrO₂Cl₂, VOCl₃), especially ofphosphorus oxyhalides (e.g. POCl₃), phosphoric and phosphorous acidesters (e.g. di- and tri-methyl and di- and tri-ethyl phosphite) and ofamino-group-containing organyl silicon compounds (e.g.3-aminopropyl-triethoxy- and -trimethoxy-silane).

Layers of oxides of the metals zirconium, titanium, iron and zinc, oxidehydrates of those metals, iron titanates, titanium suboxides or mixturesthereof are preferably applied by precipitation by a wet chemicalmethod, it being possible, where appropriate, for the metal oxides to bereduced. In the case of the wet chemical coating, the wet chemicalcoating methods developed for the production of pearlescent pigments maybe used; these are described, for example, in DE-A-14 67 468, DE-A-19 59988, DE-A-20 09 566, DE-A-22 14 545, DE-A-22 15 191, DE-A-22 44 298,DE-A-23 13 331, DE-A-25 22 572, DE-A-31 37 808, DE-A-31 37 809, DE-A-3151 343, DE-A-31 51 354, DE-A-31 51 355, DE-A-32 11 602 and DE-A-32 35017, DE 195 99 88, WO 93/08237, and WO 98/53001.

For the purpose of coating, the substrate particles are suspended inwater and one or more hydrolysable metal salts are added at a pHsuitable for the hydrolysis, which is so selected that the metal oxidesor metal oxide hydrates are precipitated directly onto the particleswithout subsidiary precipitation occurring. The pH is usually keptconstant by simultaneously metering in a base. The pigments are thenseparated off, washed, dried and, where appropriate, baked, it beingpossible to optimise the baking temperature with respect to the coatingin question. If desired, after individual coatings have been applied,the pigments can be separated off, dried and, where appropriate, baked,and then again re-suspended for the purpose of precipitating furtherlayers.

The metal oxide layers are obtainable, for example, in analogy to amethod described in DE-A-195 01 307, by producing the metal oxide layerby controlled hydrolysis of one or more metal acid esters, whereappropriate in the presence of an organic solvent and a basic catalyst,by means of a sol-gel process. Suitable basic catalysts are, forexample, amines, such as triethylamine, ethylenediamine, tributylamine,dimethylethanolamine and methoxy-propylamine. The organic solvent is awater-miscible organic solvent such as a C₁₋₄ alcohol, especiallyisopropanol.

Suitable metal acid esters are selected from alkyl and aryl alcoholates,carboxylates, and carboxyl-radical- or alkyl-radical- oraryl-radical-substituted alkyl alcoholates or carboxylates of vanadium,titanium, zirconium, silicon, aluminium and boron. The use oftriisopropyl aluminate, tetraisopropyl titanate, tetraisopropylzirconate, tetraethyl orthosilicate and triethyl borate is preferred. Inaddition, acetylacetonates and acetoacetylacetonates of theaforementioned metals may be used. Preferred examples of that type ofmetal acid ester are zirconium acetylacetonate, aluminiumacetylacetonate, titanium acetylacetonate and diisobutyloleylacetoacetylaluminate or diisopropyloleyl acetoacetylacetonate andmixtures of metal acid esters, for example Dynasil® (Hüls), a mixedaluminium/silicon metal acid ester.

As a metal oxide having a high refractive index, titanium dioxide ispreferably used, the method described in U.S. Pat. No. 3,553,001 beingused, in accordance with an embodiment of the present invention, forapplication of the titanium dioxide layers.

An aqueous titanium salt solution is slowly added to a suspension of thematerial being coated, which suspension has been heated to about 50-100°C., especially 70-80° C., and a substantially constant pH value of aboutfrom 0.5 to 5, especially about from 1.2 to 2.5, is maintained bysimultaneously metering in a base such as, for example, aqueous ammoniasolution or aqueous alkali metal hydroxide solution. As soon as thedesired layer thickness of precipitated TiO₂ has been achieved, theaddition of titanium salt solution and base is stopped.

This method, also referred to as a titration method, is distinguished bythe fact that an excess of titanium salt is avoided. That is achieved byfeeding in for hydrolysis, per unit time, only that amount which isnecessary for even coating with the hydrated TiO₂ and which can be takenup per unit time by the available surface of the particles being coated.In principle, the anatase form of TiO₂ forms on the surface of thestarting pigment By adding small amounts of SnO₂, however, it ispossible to force the rutile structure to be formed. For example, asdescribed in WO 93/08237, tin dioxide can be deposited before titaniumdioxide precipitation and the product coated with titanium dioxide canbe cacined at from 800 to 900° C.

Where appropriate, an SiO₂ protective layer can be applied on top of thetitanium dioxide layer, for which the following method may be used: Asoda waterglass solution is metered in to a suspension of the materialbeing coated, which suspension has been heated to about 50-100° C.,especially 70-80° C. The pH is maintained at from 4 to 10, preferablyfrom 6.5 to 8.5, by simultaneously adding 10% hydrochloric acid. Afteraddition of the waterglass solution, stirring is carried out for 30minutes.

It is possible to obtain pigments that are more intense in colour andmore transparent by applying, on top of the TiO₂ layer, a metal oxide of“low” refractive index, that is to say a refractive index smaller thanabout 1.65, such as SiO₂, Al₂O₃, AlOOH, B₂O₃ or a mixture thereof,preferably SiO₂, and applying a further Fe₂O₃ and/or TiO₂ layer on topof the latter layer. Such multi-coated interference pigments comprisinga silicon/silicon oxide substrate and alternating metal oxide layers ofwith high and low refractive index can be prepared in analogy to theprocesses described in WO98/53011 and WO99/20695.

It is, in addition, possible to modify the powder colour of the pigmentby applying further layers such as, for example, coloured metal oxidesor Berlin Blue, compounds of transition metals, e.g. Fe, Cu, Ni, Co, Cr,or organic compounds such as dyes or colour lakes.

It is furthermore possible to subject the finished pigment to subsequentcoating or subsequent treatment which further increases the light,weather and chemical stability or which facilitates handling of thepigment, especially its incorporation into various media. For example,the procedures described in DE-A-22 15 191, DE-A-31 51 354, DE-A-32 35017 or DE-A-33 34 598 are suitable as subsequent treatment or subsequentcoating.

In addition, the pigment according to the invention can also be coatedwith poorly soluble, firmly adhering, inorganic or organic colourants.Preference is given to the use of colour lakes and, especially,aluminium colour lakes. For that purpose an aluminium hydroxide layer isprecipitated, which is, in a second step, laked by using a colour lake(DE-A-24 29 762 and DE 29 28 287).

Furthermore, the pigment according to the invention may also have anadditional coating with complex salt pigments, especially cyanoferratecomplexes (EP-A-141 173 and DE-A-23 13 332).

In a further preferred embodiment, the pigment comprises in this order:

-   (a1) a silicon/silicon oxide layer obtainable by heating a SiO_(x)    layer, especially a SiO_(y) layer in an oxygen-free atmosphere at a    temperature above 400° C.,-   (b1) a reflective layer, especially a metal layer, and-   (c1) a silicon/silicon oxide layer obtainable by heating a SiO_(x)    layer, especially a SiO_(y) layer in an oxygen-free atmosphere at a    temperature above 400° C., wherein 0.70≦y≦1.8 and optionally further    layers.

The pigments obtainable by heating SiO/reflective material/SiO_(y)particles and comprising layers (a1), (b1) and (c1) are prepared by aprocess comprising the steps:

-   a) vapour-deposition of a separating agent onto a movable carrier to    produce a separating agent layer,-   b1) vapour-deposition of an SiO_(y) layer onto the separating agent    layer, wherein 0.70≦y≦1.8, preferably wherein 0.70≦y≦0.99 or    1.0≦y≦1.8, especially wherein 1.1≦y≦1.8,-   b2) vapour-deposition of a reflective material, especially    aluminium, onto the layer obtained in step (b1),-   b3) vapour-deposition of an SiO_(y) layer onto the metal layer,-   c) dissolution of the separating agent layer in a solvent,-   d) separation of the SiO/reflective material/SiO_(y) particles from    the solvent, and-   e) heating the SiO_(y)/reflective material/SiO_(y) particles in an    oxygen-free atmosphere to a temperature above 400° C.

If step (b3) is omitted, unsymmetrical pigments comprising layers (a1)and (b1) are obtained.

In a preferred embodiment, the above pigment comprises a further layerof a dielectric material having a “high” refractive index, that is tosay a refractive index greater than about 1.65, which is applied to theentire surface of the (silicon/silicon oxide)/reflectivematerial/(silicon/silicon oxide) substrate (see above). The dielectricmaterial is preferably a metal oxide, it being possible for the metaloxide to be a single oxide or a mixture of oxides, with or withoutabsorbing properties, for example CeO₂, TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃or ZnO, with CeO₂, TiO₂, and ZrO₂ being especially preferred.

The reflective layer consists preferably of a metallic reflectingmaterial, especially Ag, Al, Au, Cu, Cr, Ge, Mo, Ni, Si, Ti, the alloysthereof, graphite, Fe₂O₃ or MoS₂, particularly preferably Al or MoS₂. IfAl forms the reflective layer and the reflective layer should beretained, temperatures above 600° C. should be avoided to preventreaction of the Al with silicon and/or silicon oxide contained in theneighbouring layers. If Al forms the reflective layer and the flakes areheated to temperatures above 600° C., the Al reacts with silicon and/orsilicon oxide contained in the neighbouring layers and the reflectivelayer is converted into a transparent aluminum silicate layer.

If Al is used as metal of layer (b1), the thickness of layer (b1) isgenerally 20 to 100 nm, especially 40 to 60 nm. The Al is evaporated attemperatures of more than 1000° C.

The thickness of layers (a1) and (c1) is generally 2 to 500 nm,especially 50 to 300 nm.

In addition, after heat-treatment in an oxygen-free atmosphere, theflakes can be subjected to oxidative heat treatment in air or some otheroxygen-containing gas at a temperature of more than 200° C., preferablymore than 400° C. and especially from 500 to 1000° C.

It is furthermore possible to convert plane-parallel structures ofsilicon/silicon oxide, starting from their surface, partially to siliconcarbide (SiC) (in the context of the present Application, this procedureshall be referred to as “carburisation”; see PCT/EP03/01323). Thisprocessing step results in modified chemical and mechanical properties.

After partial conversion to SiC, the surface of the plane-parallelstructures is distinguished, in comparison to silicon oxide, by greaterhardness, reduced electrical insulation properties and reflection in theinfra-red of up to 80% as opposed to reflection of 8% in the case ofSiO₂ structures. In accordance with the invention, the conversion iscarried out on all sides, that is to say even at the side edges of thestructures. Such a conversion makes use of the fact that silicon oxidereacts at elevated temperature in the presence of carbon-containinggases to form SiC. The plane-parallel structures obtained by such meansare novel and the present invention relates also thereto.

Consequently, the present invention relates also to plane-parallelstructures (pigments) based on plane-parallel silicon/silicon oxidesubstrates having on their surface a layer comprising silicon carbide(SiC). The SiO_(y)-to-SiC reaction takes place starting from the surfaceof the plane-parallel structures and accordingly results in a gradientrather than a sharp transition. This means that, in that embodiment, theSiC-containing layer consists of (silicon/silicon oxide)_(n) and(SiC)_(b), wherein 0≦a<1 and 0<b≦1, with b being 1 and a being 0 closeto the surface of the pigment and the amount of SiC approaching 0 closeto the boundary with the silicon/silicon oxide substrate.

For that purpose, the SiO_(y) flakes, after they have been heated in anoxygen-free atmosphere, preferably Argon, at a temperature above 400°C., especially above 900° C., are caused to react in a gas-tight reactorheatable to a maximum of about 1500° C., preferably in the form of loosematerial, with a carbon-containing gas selected from alkynes, forexample acetylene, alkanes, for example methane, alkenes, aromaticcompounds or the like, and mixtures thereof optionally in admixture withan oxygen containing compound, such as, for example, aldehydes, ketones,water, carbon monoxide, carbon dioxide or the like, or mixtures thereof,at from 500 to 1500° C., preferably from 500 to 1000° C., andadvantageously with the exclusion of oxygen. In order to temper thereaction, an inert gas, for example argon or helium, may be admixed withthe carbon-containing gas.

At temperatures of less than about 500° C., that reaction generallyproceeds too slowly whereas temperatures of more than about 1500° C.necessitate expensive lining of the reaction vessel with inert materialssuch as SiC, carbon, graphite or composite materials thereof. Atpressures of less than about 1 Pa the reaction generally also proceedstoo slowly whereas, especially when the carbon-containing gases are lessreactive or are highly diluted with inert gas, it is perfectly possibleto operate at pressures of up to about 4000 bar, as are routinely used,for example, in HIP (“hot isostatic pressing”) systems.

In such carburisation, it is possible for all of the SiO_(y) to bereacted to form SiC; preferably from 5 to 90% by weight of the SiO_(y)are reacted to form SiC.

After carbide formation has been terminated, it is possible, optionally,for residual silicon oxide still present in the plane-parallelstructures to be converted into SiO₂ by oxidation with anoxygen-containing gas, without destroying the SiC formed. Because of thelarge specific surface area of the plane-parallel structures,temperatures of about 400° C. should not, in this case, be exceeded inthe presence of oxygen. The thickness of the structures produced inaccordance with the invention is from 20 to 2000 nm, preferably, from 20to 500 nm for most applications. Complete conversion of SiC into SiO₂would be the consequence if an excessively high oxidation temperaturewere to be used.

The present invention relates furthermore to novel (plane-parallel)pigments based on SiO_(z) substrates in platelet form having, on thesurface of the SiO_(z) substrates, wherein 0.95≦z≦2, a layer comprisingsilicon carbide (SiC). The pigments are highly shear-stable and, inplastics, surface coatings or printing inks, result in high degrees ofsaturation and excellent fastness properties and also, in the case ofinterference pigments, a high degree of goniochromicity.

The pigment particles generally have a length of from 1 μm to 5 mm, awidth of from 1 μm to 2 mm, and a thickness of from 20 nm to 1.5 μm, anda ratio of length to thickness of at least 2:1, the particles having acore of SiO_(z) having two substantially parallel faces, the distancebetween which is the shortest axis of the core, and having anSiC-containing layer applied to the entire surface of the core and,optionally, further layers. In a preferred embodiment, the pigmentcomprises a further layer of a dielectric material having a “high”refractive index, that is to say a refractive index greater than about1.65, which is applied to the entire surface of the SiC/silicon/siliconoxide substrate (see above). The dielectric material is preferably ametal oxide, it being possible for the metal oxide to be a single oxideor a mixture of oxides, with or without absorbing properties, forexample CeO₂, TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃ or ZnO, with CeO₂, TiO₂,and ZrO₂ being especially preferred.

In this embodiment the thickness of the SiC/(silicon/silicon oxide)flakes is generally from 20 to 1000 nm, preferably from 20 to 500 nm,and that of the TiO₂ layer generally from 1 to 100 nm, preferably from 5to 50 nm.

Instead of a layer of a metal oxide having a high index of refractionU.S. Pat. No. 6,524,381 materials, such as diamond-like carbon andamorphous carbon, can be deposited by plasma-assisted vacuum methods(using vibrating conveyors, rotating drum coaters, oscillatory drumcoaters, and free-fall chambers) as described, for example in U.S. Pat.No. 6,524,381, on the silicon/silicon oxide substrates.

Consequently, the present invention also relates to plane-parallelstructures (pigments) based on plane-parallel silicon/silicon oxidesubstrates having on their surface a carbon layer especially adiamond-like carbon layer having a thickness of 10 to 150 nm.

In the method described, for example, in U.S. Pat. No. 6,015,597,diamond-like network (DLN) coatings are deposited onto particles fromcarbon-containing gases, such as, for example, acetylene, methane,butadiene and mixtures of these and optionally Ar, and optionally gasescontaining additional components by plasma deposition. Deposition occursat reduced pressures (relative to atmospheric pressure) and in acontrolled environment. A carbon rich plasma is created in a reactionchamber by applying an electric field to a carbon-containing gas.Particles to be coated are held in a vessel or container in the reactorand are agitated while in proximity to the plasma. Species within theplasma react on the particle surface to form covalent bonds, resultingin DLN on the surface of the particles.

The term “diamond-like network” (DLN) refers to amorphous films orcoatings comprised of carbon and optionally comprising one or moreadditional components selected from the group consisting of hydrogen,nitrogen, oxygen, fluorine, silicon, sulfur, titanium, and copper.

The diamond-like networks comprise approximately 30 to 100 atomicpercent carbon, with optional additional components making up theremainder.

In a further preferred embodiment, the pigment comprises in this order:

-   (a2) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.70-0.99) layer in an oxygen-free atmosphere at a temperature    above 400° C.,-   (b2) a silicon/silicon oxide layer obtainable by heating a    SiO_(1.00-1.8) layer in an oxygen-free atmosphere at a temperature    above 400° C., and-   (c2) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.07-0.99) layer in an oxygen-free atmosphere at a temperature    above 400° C. and optionally further layers.

The pigments comprising layers (a2), (b2) and (c2) are prepared by aprocess comprising the steps:

-   a) vapour-deposition of a separating agent onto a movable carrier to    produce a separating agent layer,-   b1) vapour-deposition of a SiO_(y) layer onto the separating agent    layer, wherein 0.70≦y≦0.99,-   b2) vapour-deposition of a SiO_(y) layer, wherein 1.0≦y≦1.8 onto the    layer obtained in step (b1),-   b3) vapour-deposition of a SiO_(y) layer onto the layer obtained in    step (b2),-   c) dissolution of the separating agent layer in a solvent,-   d) separation of the SiO_(y)/SiO_(y) particles from the solvent, and-   e) heating the SiO_(0.70-0.99)/SiO_(1.0-1.8)/SiO_(0.70-0.99)    particles in an oxygen-free atmosphere to a temperature above 400°    C.

If step (b3) is omitted, unsymmetrical pigments comprising layers (a2)and (b2) are obtained.

The SiO_(1.00-1.8) layer in step b) is formed preferably from siliconmonoxide vapour produced in the vaporiser by reaction of a mixture of Siand SiO₂ at temperatures of more than 1300° C.

The SiO_(70.0-0.99) layer in step b) is formed preferably by evaporatingsilicon monoxide containing silicon in an amount up to 20% by weight attemperatures of more than 1300° C.

It is possible, for example, for the weathering resistance to beincreased by means of an additional protective layer, from 2 to 250 nmthick (preferably from 10 to 100 nm thick), of an inorganic dielectrichaving a refractive index ≦1.6 (such as SiO₂, SiO(OH)₂ etc.).

In a preferred embodiment, the pigment comprises a further layer of adielectric material having a “high” refractive index, that is to say arefractive index greater than about 1.65, which is applied to the entiresurface of the above pigment (see above). The dielectric material ispreferably a metal oxide, it being possible for the metal oxide to be asingle oxide or a mixture of oxides, with or without absorbingproperties, for example CeO₂, TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃ or ZnO,with CeO₂, TiO₂, and ZrO₂ being especially preferred.

The thickness of layer (b2) is generally 50 to 400 nm, especially 50 to300 nm.

The thickness of layers (a2) and (c2) is generally 50 to 200 nm,especially 50 to 100 nm.

In addition, after heat-treatment in an oxygen-free atmosphere, theflakes can be subjected to oxidative heat treatment in air or some otheroxygen-containing gas at a temperature of more than 200° C., preferablymore than 400° C. and especially from 500 to 1000° C.

It is furthermore possible to convert plane-parallel structures ofsilicon/silicon oxide as described above, starting from their surface,partially to silicon carbide (SiC) (in the context of the presentApplication, this procedure shall be referred to as “carburisation”; seePCT/EP03/01323). This processing step results in modified chemical andmechanical properties.

Instead of a layer of a metal oxide having a high index of refractionmaterials, such as diamond-like carbon and amorphous carbon, can bedeposited by plasma-assisted vacuum methods (using vibrating conveyors,rotating drum coaters, oscillatory drum coaters, and free-fall chambers)as described above.

In a further preferred embodiment, the pigment comprises in this order:

-   (a3) a silicon/silicon oxide layer obtainable by heating a    SiO_(1.00-1.8) layer in an oxygen-free atmosphere at a temperature    above 400° C.,-   (b3) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.07-0.99) layer in an oxygen-free atmosphere at a temperature    above 400° C., and-   (c3) a silicon/silicon oxide layer obtainable by heating a    SiO_(1.00-1.8) layer in an oxygen-free atmosphere at a temperature    above 400° C. and optionally further layers.

The pigments comprising layers (a3), (b3) and (c3) are prepared by aprocess comprising the steps:

-   a) vapour-deposition of a separating agent onto a movable carrier to    produce a separating agent layer,-   b1) vapour-deposition of a SiO_(y) layer onto the separating agent    layer, wherein 1.0≦y≦1.8,-   b2) vapour-deposition of a SiO_(y) layer, wherein 0.70≦y≦0.99, onto    the layer obtained in step (b1),-   b3) vapour-deposition of a SiO_(y), wherein 1.0≦y≦1.8, layer onto    the metal layer obtained in step (b2),-   c) dissolution of the separating agent layer in a solvent,-   d) separation of the SiO/Al/SiO_(y) particles from the solvent, and-   e) heating the SiO_(0.70-099)/SiO_(1.0-1.8)/SiO_(0.70-0.99)    particles in an oxygen-free atmosphere to a temperature above 400°    C.

The SiO_(1.00-1.8) layer in step b1) and b3) is formed preferably fromsilicon monoxide vapour produced in the vaporiser by reaction of amixture of Si and SiO₂ at temperatures of more than 1300° C.

The SiO_(0.70-0.99) layer in step b2) is formed preferably byevaporating silicon monoxide containing silicon in an amount up to 20%by weight at temperatures of more than 1300° C.

If step (b3) is omitted, unsymmetrical pigments comprising layers (a3)and (b3) are obtained.

It is possible, for example, for the weathering resistance to beincreased by means of an additional protective layer, from 2 to 250 nmthick (preferably from 10 to 100 nm thick), of an inorganic dielectrichaving a refractive index ≦1.6 (such as SiO₂, SiO(OH)₂ etc.). Such alayer can be formed, for example, by oxidative heat treatment of thebasis pigment.

In a preferred embodiment, the pigment comprises a further layer of adielectric material having a ‘high’ refractive index, that is to say arefractive index greater than about 1.65, which is applied to the entiresurface of the silicon/silicon oxide/reflective material/silicon/siliconoxide substrate (see above). The dielectric material is preferably ametal oxide, it being possible for the metal oxide to be a single oxideor a mixture of oxides, with or without absorbing properties, forexample CeO₂, TiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃ or ZnO, with CeO₂, TiO₂,and ZrO₂ being especially preferred.

The thickness of layer (b2) is generally 50 to 400 nm, especially 100 to300 nm.

The thickness of layers (a3) and (c3) is generally 50 to 200 nm,especially 50 to 100 nm.

In addition, after heat-treatment in an oxygen-free atmosphere, theflakes can be subjected to oxidative heat treatment in air or some otheroxygen-containing gas at a temperature of more than 200° C., preferablymore than 400° C. and especially from 500 to 1000° C.

If, under industrial vacuums of a few 10⁻² Pa, Si is vaporised (insteadof Si/SiO₂ or SiO/Si) silicon oxides can be obtained which have anoxygen content of less than 0.70, that is to say SiO_(x) wherein0.03≦x≦0.69, especially 0.05≦x≦0.50, very especially 0.10≦x≦0.30(PCT/EP03/02196).

Accordingly, in a further preferred embodiment, the pigment comprises inthis order:

-   (a4) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperature    above 400° C.,-   (b4) a silicon/silicon oxide layer obtainable by heating a    SiO_(1.00-1.8) layer in an oxygen-free atmosphere at a temperature    above 400° C., and-   (c4) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperature    above 400° C., and optionally further layers, or the pigment    comprises in this order:-   (a5) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperature    above 400° C.,-   (b5) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.70-0.99) layer in an oxygen-free atmosphere at a temperature    above 400° C., and-   (c5) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperature    above 400° C., and optionally further layers.

Heating in the presence of oxygen at from 150 to 500° C., preferablyfrom 175 to 300° C., unexpectedly results in a very thin, e.g.approximately 20 nm thick, superficial silicon dioxide layer, whichrepresents a very convenient method of producing structures having thelayer sequence SiO₂/(a4)/(b4)/(c4)/SiO₂.

In a further preferred embodiment, the pigment comprises in this order:

-   (a6) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.70-0.99) layer in an oxygen-free atmosphere at a temperature    above 400° C.,-   (b6) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperature    above 400° C., and-   (c6) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.70-0.99) layer in an oxygen-free atmosphere at a temperature    above 400° C. and optionally further layers, or-   (a7) a silicon/silicon oxide layer obtainable by heating a    SiO_(1.00-1.80) layer in an oxygen-free atmosphere at a temperature    above 400° C.,-   (b7) a silicon/silicon oxide layer obtainable by heating a    SiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperature    above 400° C., and-   (c7) a silicon/silicon oxide layer obtainable by heating a    SiO_(1.00-1.80) layer in an oxygen-free atmosphere at a temperature    above 400° C. and optionally further layers.

It is furthermore possible to convert plane-parallel structures ofsilicon/silicon oxide as described above, starting from their surface,partially to silicon carbide (SiC) (in the context of the presentApplication, this procedure shall be referred to as “carburisation”; seePCT/EP03/01323). This processing step results in modified chemical andmechanical properties.

Instead of a layer of a metal oxide having a high index of refractionmaterials, such as diamond-like carbon and amorphous carbon, can bedeposited by plasma-assisted vacuum methods (using vibrating conveyors,rotating drum coaters, oscillatory drum coaters, and free-fall chambers)as described above.

In certain embodiments, for example, pigments may be chosen from thestructures (X=silicon/silicon oxide layer, obtainable by heatingplane-parallel structures of SiO_(y) in an oxygen-free atmosphere at atemperature above 400° C., wherein 0.70≦y≦1.8): X/Al/X, C/X/Al/X/C,X/C/X/C/X, C/X/C/X/C, Al/X/Al/X/Al; Cr/X/Al/X/Cr; MoS₂/X/Al/X/Mos₂;Fe₂/X/Al/X/Fe₂O₃; MoS₂/X/mica-oxide/X/MoS₂; andFe₂O₃/X/mica-oxide/X/Fe₂O₃.

Various forms of carbon (C) can be utilized in the present invention,including but not limited to, graphitic, carbonaceous, and amorphouscarbon; vitreous carbon; diamond-like carbon; amorphous hydrogenatedcarbon such as amorphous hydrogenated diamond-like carbon; carboncompounds; various combinations thereof, and the like. Other forms ofcarbon with different optical properties resulting from the method ofdeposition can also be utilized, such as arc evaporated carbon, ionassisted carbon I, and ion assisted carbon II.

The pigments according to the invention can be used for all customarypurposes, for example for colouring polymers in the mass, surfacecoatings (including effect finishes, including those for the automotivesector) and printing inks, and also, for example, for applications incosmetics. Such applications are known from reference works, for example“Industrielle Organische Pigmente” (W. Herbst and K. Hunger, VCHVerlagsgesellschaft mbH, Weinheim/New York, 2nd, completely revisededition, 1995).

When the pigments according to the invention are interference pigments(effect pigments), they are goniochromatic and result in brilliant,highly saturated (lustrous) colours. They are accordingly veryespecially suitable for combination with conventional, transparentpigments, for example organic pigments such as, for example,diketopyrrolopyrroles, quinacridones, dioxazines, perylenes,isoindolinones etc., it being possible for the transparent pigment tohave a similar colour to the effect pigment. Especially interestingcombination effects are obtained, however, in analogy to, for example,EP 388 932, or EP 402 943, when the colour of the transparent pigmentand that of the effect pigment are complementary.

The pigments according to the invention can be used with excellentresults for pigmenting high molecular weight organic material.

The high molecular weight organic material for the pigmenting of whichthe pigments or pigment compositions according to the invention may beused may be of natural or synthetic origin. High molecular weightorganic materials usually have molecular weights of about from 10³ to10⁸ g/mol or even more. They may be, for example, natural resins, dryingoils, rubber or casein, or natural substances derived therefrom, such aschlorinated rubber, oil-modified alkyd resins, viscose, cellulose ethersor esters, such as ethylcellulose, cellulose acetate, cellulosepropionate, cellulose acetobutyrate or nitrocellulose, but especiallytotally synthetic organic polymers (thermosetting plastics andthermoplastics), as are obtained by polymerisation, polycondensation orpolyaddition. From the class of the polymerisation resins there may bementioned, especially, polyolefins, such as polyethylene, polypropyleneor polyisobutylene, and also substituted polyolefins, such aspolymerisation products of vinyl chloride, vinyl acetate, styrene,acrylonitrile, acrylic acid esters, methacrylic acid esters orbutadiene, and also copolymerisation products of the said monomers, suchas especially ABS or EVA.

From the series of the polyaddition resins and polycondensation resinsthere may be mentioned, for example, condensation products offormaldehyde with phenols, so-called phenoplasts, and condensationproducts of formaldehyde with urea, thiourea or melamine, so-calledaminoplasts, and the polyesters used as surface-coating resins, eithersaturated, such as alkyd resins, or unsaturated, such as maleate resins;also linear polyesters and polyamides, polyurethanes or silicones.

The said high molecular weight compounds may be present singly or inmixtures, in the form of plastic masses or melts. They may also bepresent in the form of their monomers or in the polymerised state indissolved form as film-formers or binders for surface coatings orprinting inks, such as, for example, boiled linseed oil, nitrocellulose,alkyd resins, melamine resins and urea-formaldehyde resins or acrylicresins.

Depending on the intended purpose, it has proved advantageous to use thepigments or pigment compositions according to the invention as toners orin the form of preparations.

Depending on the conditioning method or intended application, it may beadvantageous to add certain amounts of texture-improving agents to thepigment before or after the conditioning process, provided that this hasno adverse effect on use of the effect pigments for colouring highmolecular weight organic materials, especially polyethylene. Suitableagents are, especially, fatty acids containing at least 18 carbon atoms,for example stearic or behenic acid, or amides or metal salts thereof,especially magnesium salts, and also plasticisers, waxes, resin acids,such as abietic acid, rosin soap, alkylphenols or aliphatic alcohols,such as stearyl alcohol, or aliphatic 1,2-dihydroxy compounds containingfrom 8 to 22 carbon atoms, such as 1,2-dodecanediol, and also modifiedcolophonium maleate resins or fumaric acid colophonium resins. Thetexture-improving agents are added in amounts of preferably from 0.1 to30% by weight, especially from 2 to 15% by weight, based on the endproduct.

The pigments according to the invention can be added in any tinctoriallyeffective amount to the high molecular weight organic material beingpigmented. A pigmented substance composition comprising a high molecularweight organic material and from 0.01 to 80% by weight, preferably from0.1 to 30% by weight, based on the high molecular weight organicmaterial, of an pigment according to the invention is advantageous.Concentrations of from 1 to 20% by weight, especially of about 10% byweight, can often be used in practice.

High concentrations, for example those above 30% by weight, are usuallyin the form of concentrates (“masterbatches”) which can be used ascolorants for producing pigmented materials having a relatively lowpigment content, the pigments according to the invention having anextraordinarily low viscosity in customary formulations so that they canstill be processed well.

For the purpose of pigmenting organic materials, the pigments accordingto the invention may be used singly. It is, however, also possible, inorder to achieve different hues or colour effects, to add any desiredamounts of other colour-imparting constituents, such as white, coloured,black or effect pigments, to the high molecular weight organicsubstances in addition to the effect pigments according to theinvention. When coloured pigments are used in admixture with the effectpigments according to the invention, the total amount is preferably from0.1 to 10% by weight, based on the high molecular weight organicmaterial. Especially high goniochromicity is provided by the preferredcombination of an effect pigment according to the invention with acoloured pigment of another colour, especially of a complementarycolour, with colorations made using the effect pigment and colorationsmade using the coloured pigment having, at a measurement angle of 10°, adifference in hue (ΔH*) of from 20 to 340, especially from 150 to 210.

Preferably, the effect pigments according to the invention are combinedwith transparent coloured pigments, it being possible for thetransparent coloured pigments to be present either in the same medium asthe effect pigments according to the invention or in a neighbouringmedium. An example of an arrangement in which the effect pigment and thecoloured pigment are advantageously present in neighbouring media is amulti-layer effect surface coating.

The pigmenting of high molecular weight organic substances with thepigments according to the invention is carried out, for example, byadmixing such a pigment, where appropriate in the form of a masterbatch,with the substrates using roll mills or mixing or grinding apparatuses.The pigmented material is then brought into the desired final form usingmethods known per se, such as calendering, compression moulding,extrusion, coating, pouring or injection moulding. Any additivescustomary in the plastics industry, such as plasticisers, fillers orstabilisers, can be added to the polymer, in customary amounts, beforeor after incorporation of the pigment. In particular, in order toproduce non-rigid shaped articles or to reduce their brittleness, it isdesirable to add plasticisers, for example esters of phosphoric acid,phthalic acid or sebacic acid, to the high molecular weight compoundsprior to shaping.

For pigmenting surface coatings and printing inks, the high molecularweight organic materials and the pigments according to the invention,where appropriate together with customary additives such as, forexample, fillers, other pigments, siccatives or plasticisers, are finelydispersed or dissolved in the same organic solvent or solvent mixture,it being possible for the individual components to be dissolved ordispersed separately or for a number of components to be dissolved ordispersed together, and only thereafter for all the components to bebrought together.

Dispersing an pigment according to the invention in the high molecularweight organic material being pigmented, and processing a pigmentcomposition according to the invention, are preferably carried outsubject to conditions under which only relatively weak shear forcesoccur so that the effect pigment is not broken up into smaller portions.

The colorations obtained, for example in plastics, surface coatings orprinting inks, especially in surface coatings or printing inks, moreespecially in surface coatings, are distinguished by excellentproperties, especially by extremely high saturation, outstandingfastness properties and high goniochromicity.

When the high molecular weight material being pigmented is a surfacecoating, it is especially a speciality surface coating, very especiallyan automotive finish.

The pigments according to the invention are also suitable for making-upthe lips or the skin and for colouring the hair or the nails.

The invention accordingly relates also to a cosmetic preparation orformulation comprising from 0.0001 to 90% by weight of thesilicon/silicon oxide flakes and/or of a pigment according to theinvention and from 10 to 99.9999% of a cosmetically suitable carriermaterial, based on the total weight of the cosmetic preparation orformulation.

Such cosmetic preparations or formulations are, for example, lipsticks,blushers, foundations, nail varnishes and hair shampoos.

The pigments may be used singly or in the form of mixtures. It is, inaddition, possible to use pigments according to the invention togetherwith other pigments and/or colorants, for example in combinations asdescribed hereinbefore or as known in cosmetic preparations.

The cosmetic preparations and formulations according to the inventionpreferably contain the pigment according to the invention in an amountfrom 0.005 to 50% by weight, based on the total weight of thepreparation.

Suitable carrier materials for the cosmetic preparations andformulations according to the invention include the customary materialsused in such compositions.

The cosmetic preparations and formulations according to the inventionmay be in the form of, for example, sticks, ointments, creams,emulsions, suspensions, dispersions, powders or solutions. They are, forexample, lipsticks, mascara preparations, blushers, eye-shadows,foundations, eyeliners, powder or nail varnishes.

If the preparations are in the form of sticks, for example lipsticks,eye-shadows, blushers or foundations, the preparations consist for aconsiderable part of fatty components, which may consist of one or morewaxes, for example ozokerite, lanolin, lanolin alcohol, hydrogenatedlanolin, acetylated lanolin, lanolin wax, beeswax, candelilla wax,microcrystalline wax, carnauba wax, cetyl alcohol, stearyl alcohol,cocoa butler, lanolin fatty acids, petrolatum, petroleum jelly, mono-,di- or tri-glycerides or fatty esters thereof that are solid at 25° C.,silicone waxes, such as methyloctadecane-oxypolysiloxane andpoly(dimethylsiloxy)-stearoxysiloxane, stearic acid monoethanolamine,colophane and derivatives thereof, such as glycol abietates and glycerolabietates, hydrogenated oils that are solid at 25° C., sugar glyceridesand oleates, myristates, lanolates, stearates and dihydroxystearates ofcalcium, magnesium, zirconium and aluminium.

The fatty component may also consist of a mixture of at least one waxand at least one oil, in which case the following oils, for example, aresuitable: paraffin oil, purcelline oil, perhydrosqualene, sweet almondoil, avocado oil, calophyllum oil, castor oil, sesame oil, jojoba oil,mineral oils having a boiling point of about from 310 to 410° C.,silicone oils, such as dimethylpolysiloxane, linoleyl alcohol, linolenylalcohol, oleyl alcohol, cereal grain oils, such as wheatgerm oil,isopropyl lanolate, isopropyl palmitate, isopropyl myristate, butylmyristate, cetyl myristate, hexadecyl stearate, butyl stearate, decyloleate, acetyl glycerides, octanoates and decanoates of alcohols andpolyalcohols, for example of glycol and glycerol, ricinoleates ofalcohols and polyalcohols, for example of cetyl alcohol, isostearylalcohol, isocetyl lanolate, isopropyl adipate, hexyl laurate and octyldodecanol.

The fatty components in such preparations in the form of sticks maygenerally constitute up to 99.91% by weight of the total weight of thepreparation.

The cosmetic preparations and formulations according to the inventionmay additionally comprise further constituents, such as, for example,glycols, polyethylene glycols, polypropylene glycols, monoalkanolamides,non-coloured polymeric, inorganic or organic fillers, preservatives, UVfilters or other adjuvants and additives customary in cosmetics, forexample a natural or synthetic or partially synthetic di- ortri-glyceride, a mineral oil, a silicone oil, a wax, a fatty alcohol, aGuerbet alcohol or ester thereof, a lipophilic functional cosmeticactive ingredient, including sun-protection filters, or a mixture ofsuch substances.

A lipophilic functional cosmetic active ingredient suitable for skincosmetics, an active ingredient composition or an active ingredientextract is an ingredient or a mixture of ingredients that is approvedfor dermal or topical application The following may be mentioned by wayof example:

-   -   active ingredients having a cleansing action on the skin surface        and the hair; these include all substances that serve to cleanse        the skin, such as oils, soaps, synthetic detergents and solid        substances;    -   active ingredients having a deodorising and        perspiration-inhibiting action: they include antiperspirants        based on aluminium salts or zinc salts, deodorants comprising        bactericidal or bacteriostatic deodorising substances, for        example triclosan, hexachlorophene, alcohols and cationic        substances, such as, for example, quaternary ammonium salts, and        odour absorbers, for example ®Grillocin (combination of zinc        ricinoleate and various additives) or triethyl citrate        (optionally in combination with an antioxidant, such as, for        example, butyl hydroxytoluene) or ion-exchange resins;    -   active ingredients that offer protection against sunlight (UV        filters): suitable active ingredients are filter substances        (sunscreens) that are able to absorb UV radiation from sunlight        and convert it into heat; depending on the desired action, the        following light-protection agents are preferred:        light-protection agents that selectively absorb sunburn-causing        high-energy UV radiation in the range of approximately from 280        to 315 nm (UV-B absorbers) and transmit the longer-wavelength        range of, for example, from 315 to 400 nm (UV-A range), as well        as light-protection agents that absorb only the        longer-wavelength radiation of the UV-A range of from 315 to 400        nm (UV-A absorbers); suitable light-protection agents are, for        example, organic UV absorbers from the class of the        p-aminobenzoic acid derivatives, salicylic acid derivatives,        benzophenone derivatives, dibenzoylmethane derivatives, diphenyl        acrylate derivatives, benzofuran derivatives, polymeric UV        absorbers comprising one or more organosilicon radicals,        cinnamic acid derivatives, camphor derivatives,        trianilino-s-triazine derivatives, phenyl-benzimidazolesulfonic        acid and salts thereof, menthyl anthranilates, benzotriazole        derivatives, and/or an inorganic micropigment selected from        aluminium oxide- or silicon dioxide-coated TiO₂, zinc oxide or        mica;    -   active ingredients against insects (repellents) are agents that        are intended to prevent insects from touching the skin and        becoming active there; they drive insects away and evaporate        slowly; the most frequently used repellent is diethyl toluamide        (DEET); other common repellents will be found, for example, in        “Pflegekosmetik” (W. Raab and U. Kindl, Gustav-Fischer-Verlag        Stuttgart/New York, 1991) on page 161;    -   active ingredients for protection against chemical and        mechanical influences: these include all substances that form a        barrier between the skin and external harmful substances, such        as, for example, paraffin oils, silicone oils, vegetable oils,        PCL products and lanolin for protection against aqueous        solutions, film-forming agents, such as sodium alginate,        triethanolamine alginate, polyacrylates, polyvinyl alcohol or        cellulose ethers for protection against the effect of organic        solvents, or substances based on mineral oils, vegetable oils or        silicone oils as “lubricants” for protection against severe        mechanical stresses on the skin;    -   moisturising substances: the following substances, for example,        are used as moisture-controlling agents (moisturisers): sodium        lactate, urea, alcohols, sorbitol, glycerol, propylene glycol,        collagen, elastin and hyaluronic acid;    -   active ingredients having a keratoplastic effect: benzoyl        peroxide, retinoic acid, colloidal sulfur and resorcinol;    -   antimicrobial agents, such as, for example, triclosan or        quaternary ammonium compounds;    -   oily or oil-soluble vitamins or vitamin derivatives that can be        applied dermally: for example vitamin A (retinol in the form of        the free acid or derivatives thereof), panthenol, pantothenic        acid, folic acid, and combinations thereof, vitamin E        (tocopherol), vitamin F;    -   essential fatty acids; or niacinamide (nicotinic acid amide);    -   vitamin-based placenta extracts: active ingredient compositions        comprising especially vitamins A, C, E, B₁, B₂, B₆, B₁₂, folic        acid and biotin, amino acids and enzymes as well as compounds of        the trace elements magnesium, silicon, phosphorus, calcium,        manganese, iron or copper;    -   skin repair complexes: obtainable from inactivated and        disintegrated cultures of bacteria of the bifidus group;    -   plants and plant extracts: for example arnica, aloe, beard        lichen, ivy, stinging nettle, ginseng, henna, camomile,        marigold, rosemary, sage, horsetail or thyme;    -   animal extracts: for example royal jelly, propolis, proteins or        thymus extracts;    -   cosmetic oils that can be applied dermally: neutral oils of the        Miglyol 812 type, apricot kernel oil, avocado oil, babassu oil,        cottonseed oil, borage oil, thistle oil, groundnut oil,        gamma-oryzanol, rosehip-seed oil, hemp oil, hazelnut oil,        blackcurrant-seed oil, jojoba oil, cherry-stone oil, salmon oil,        linseed oil, cornseed oil, macadamia nut oil, almond oil,        evening primrose oil, mink oil, olive oil, pecan nut oil, peach        kernel oil, pistachio nut oil, rape oil, rice-seed oil, castor        oil, safflower oil, sesame oil, soybean oil, sunflower oil, tea        tree oil, grapeseed oil or wheatgerm oil.

The preparations in stick form are preferably anhydrous but may incertain cases comprise a certain amount of water which, however, ingeneral does not exceed 40% by weight, based on the total weight of thecosmetic preparation.

If the cosmetic preparations and formulations according to the inventionare in the form of semi-solid products, that is to say in the form ofointments or creams, they may likewise be anhydrous or aqueous. Suchpreparations and formulations are, for example, mascaras, eyeliners,foundations, blushers, eye-shadows, or compositions for treating ringsunder the eyes.

If, on the other hand, such ointments or creams are aqueous, they areespecially emulsions of the water-in-oil type or of the oil-in-watertype that comprise, apart from the pigment, from 1 to 98.8% by weight ofthe fatty phase, from 1 to 98.8% by weight of the aqueous phase and from0.2 to 30% by weight of an emulsifier.

Such ointments and creams may also comprise further conventionaladditives, such as, for example, perfumes, antioxidants, preservatives,gel-forming agents, UV filters, colorants, pigments, pearlescent agents,non-coloured polymers as well as inorganic or organic fillers.

If the preparations are in the form of a powder, they consistsubstantially of a mineral or inorganic or organic filler such as, forexample, talcum, kaolin, starch, polyethylene powder or polyamidepowder, as well as adjuvants such as binders, colorants etc.

Such preparations may likewise comprise various adjuvants conventionallyemployed in cosmetics, such as fragrances, antioxidants, preservativesetc.

If the cosmetic preparations and formulations according to the inventionare nail varnishes, they consist essentially of nitrocellulose and anatural or synthetic polymer in the form of a solution in a solventsystem, it being possible for the solution to comprise other adjuvants,for example pearlescent agents.

In that embodiment, the coloured polymer is present in an amount ofapproximately from 0.1 to 5% by weight.

The cosmetic preparations and formulations according to the inventionmay also be used for colouring the hair, in which case they are used inthe form of shampoos, creams or gels that are composed of the basesubstances conventionally employed in the cosmetics industry and apigment according to the invention.

The cosmetic preparations and formulations according to the inventionare prepared in conventional manner, for example by mixing or stirringthe components together, optionally with heating so that the mixturesmelt.

The Examples that follow illustrate the invention without limiting thescope thereof. Unless otherwise indicated, percentages and parts arepercentages and parts by weight, respectively.

EXAMPLES Example 1

In a vacuum system which in its fundamental points is constructedanalogously to the system described in U.S. Pat. No. 6,270,840, thefollowing are vaporised, from vaporisers, in succession: sodium chloride(NaCl) as separating agent at about 900° C., and silicon monoxide (SiO)as reaction product of Si and SiO₂ at from 1350 to 1550° C. The layerthickness of NaCl is typically 30-50 nm, that of SiO_(y) being,depending on the intended purpose of the end product, from 100 to 2000nm, in the present case 215 to 385 nm. Vaporisation is carried out atabout 0.02 Pa, amounting to about 11 g of NaCl and 72 g of SiO perminute. For subsequently detaching the layers by dissolution of theseparating agent, the carrier on which vapour-deposition has taken placeis sprayed at about 3000 Pa with deionised water and treated withmechanical assistance using scrapers and with ultrasound. The NaCldissolves and the SiO_(y) layer, which is insoluble, breaks up intoflakes. The suspension is continuously removed from the dissolutionchamber and, at atmospheric pressure, is concentrated by filtration andrinsed several times with deionised water in order to remove Na⁺ and Cl⁻ions that are present. That is followed by the steps of milling, sievingand drying. All the particles have an average diameter smaller than 40microns. A molybden crucible is then filled with these SiO flakes andset in a quartz tube. The quartz tube containing the Mo crucible withthe SiO flakes is evacuated till the vacuum reaches about 13 Pa (10⁻¹Torr). Then the tube is heated stepwise from room temperature to 900° C.The quartz tube is maintained at 900° C. during at least 1 hour. Duringthe heating the color of the SiO flakes changes and the SiO powderbecomes more and more opaque. After cooling to room temperature a fullcolored powder is obtained, which shows color changes in dependence ofthe observation angle, wherein the color depends on the thickness of theSiO flakes.

The reflection colour (CIE-L*C*h) of the silicon/silicon oxide flakes isdetermined at irradiation with standard illuminant D₆₅ under a 10°observation angle. Thickness of silicon/silicon oxide flakes [nm] Color(in air) L* C* H 215 blue 27 27 270 245 blue-green 37 16 213 260 green45 17 177 385 violet 24 34 307

Example 2

Example 1 is repeated, except that instead of a mixture of Si/SiO₂ amixture of SiO containing 15% by weight Si is used. The obtained flakeshave a ratio of oxygen to silicon of ca. 0.86, a thickness of about 120nm and an average diameter smaller than 40 microns. A molybden crucibleis then filled with these SiO_(0.86) flakes and set in a quartz tube.The quartz tube containing the Mo crucible with the SiO_(0.86) flakes isevacuated till the vacuum reaches about 13 Pa (10⁻¹ Torr). Then the tubeis heated stepwise from room temperature to 900° C. The quartz tube ismaintained at 900° C. during at least 1 hour. During the heating thecolor of the silicon oxide flakes changes and the silicon oxide powderbecomes more and more opaque. After cooling to room temperature a fullcolored powder is obtained, which shows color changes in dependence ofthe observation angle (blue/violet →yellow/orange), wherein the colordepends on the thickness of the silicon oxide flakes. The plane-parallelstructures of SiO_(0.86) show photoluminescence at 890-900 nm(excitation wavelength: ˜300 nm).

Comparative Example 1

Example 1 is repeated, except that instead of a mixture of Si/SiO₂ SiOis used. The obtained yellow flakes have a ratio of oxygen to silicon ofca. 1.0 and a thickness of about 120 nm and do not show color changes independence of the observation angle.

Example 3

The silicon/silicon oxide flakes of Example 1 having a thickness of 215nm are then coated with TiO₂ using conventional wet chemistry. The TiO₂deposition is stopped when the TiO₂ thickness reaches about 30 nm. Theobtained TiO₂ coated SiO flakes show a very bright yellow-green color inair.

The reflection colour (CIE-L*C*h) of the TiO₂ coated silicon/siliconoxide flakes is determined at irradiation with standard illuminant D₆₅under a 10° observation angle. Thickness of TiO₂ coated SiO flakes ColorL* C* H 275 nm yellow-green (in air) 67 50 99 275 nm yellow (in resin)46 44 86

Example 4

In a vacuum system which in its fundamental points is constructedanalogously to the system described in U.S. Pat. No. 6,270,840, thefollowing are vaporised, from vaporisers, in succession: sodium chloride(NaCl) as separating agent at about 900° C., Si (15% by weight)/SiO (85%by weight) at from 1350 to 1550° C., silicon monoxide (SiO) as reactionproduct of Si and SiO₂ at from 1350 to 1550° C., and Si (15% byweight)/SiO (85% by weight) at from 1350 to 1550° C. The layer thicknessof NaCl is typically 30-50 nm, that of the (SiO/Si)(50-200nm)/SiO(50-400 nm)/(SiO/Si)(50-200 nm) being 180 to 800 nm. Vaporisationis carried out at about 0.02 Pa. For subsequently detaching the layersby dissolution of the separating agent, the carrier on whichvapour-deposition has taken place is sprayed at about 3000 Pa withdeionised water and treated with mechanical assistance using scrapersand with ultrasound. The NaCl dissolves and the (SiO/Si)/SiO/(SiO/Si)layer, which is insoluble, breaks up into flakes. The suspension iscontinuously removed from the dissolution chamber and, at atmosphericpressure, is concentrated by filtration and rinsed several times withdeionised water in order to remove Na⁺ and Cl⁻ ions that are present.That is followed by the steps of milling, sieving and drying. All theparticles have an average diameter smaller than 40 microns. A molybdencrucible is then filled with these (SiO/Si)/SiO/(SiO/Si) flakes and setin a quartz tube. The quartz tube containing the Mo crucible with the(SiO/Si)/SiO/(SiO/Si) flakes is evacuated till the vacuum reaches about13 Pa (10⁻¹ Torr). Then the tube is heated stepwise from roomtemperature to 900° C. The quartz tube is maintained at 900° C. duringat least 1 hour. After cooling to room temperature a full colored powderis obtained, which shows color changes in dependence of the observationangle, wherein a different concentration of Si in the SiO₂ matrix leadsto different refractive indices and, hence, interference colors.

The reflection colour (CIE-L*C*h) of the (silicon/silicon oxide)/siliconoxide/(silicon/silicon oxide) flakes is determined at irradiation withstandard illuminant D₆₅ under a 10° observation angle. Thickness ofsilicon/silicon oxide flakes [nm] Color (in air) L* C* H (SiO/Si)(60nm)/SiO(120 green/yellow 51 38 152 nm)/(SiO/Si)(60 nm)¹⁾ (SiO/Si)(60nm)/SiO(120 ochre 47 29 35 nm)/(SiO/Si)(60 nm)²⁾ (SiO/Si)(60 nm)/SiO(100green 50 33 182 nm)/(SiO/Si)(60 nm)¹⁾ SiO/Si)(60 nm)/SiO(100 Green- 4642 140 nm)/(SiO/Si)(60 nm)²⁾ yellow¹⁾product before calcination at 900° C.; color flop: green/yellow → darkgreen.²⁾product after calcination at 900° C.; color flop: ochre →green/yellow.³⁾product before calcination at 900° C.; color flop: green → red/orange.

1. Plane-parallel structures of silicon/silicon oxide, obtained heatingplane-parallel structures of SiO_(y) in an oxygen-free atmosphere at atemperature above 400° C., wherein 0.70≦y≦1.8, or plane-parallelstructures of silicon/silicon oxide, obtainable obtained by heatingplane-parallel structures of SiO_(x) in an oxygen-free atmosphere at atemperature above 400° C., wherein 0.03≦x≦0.95.
 2. A plane-parallelpigment, comprising a silicon/silicon oxide layer, obtained by heating aSiO_(y) layer in an oxygen-free atmosphere at a temperature above 400°C., wherein 0.70≦y≦1.8, or a plane-parallel pigment, comprising asilicon/silicon oxide layer, obtained by heating plane-parallelstructures of SiO_(x) in an oxygen-free atmosphere at a temperatureabove 400° C., wherein 0.03≦x≦0.95.
 3. A pigment according to claim 2,wherein the silicon/silicon oxide layer, obtained by heating a SiO_(y)layer in an oxygen-free atmosphere at a temperature above 400° C., formsthe core of the pigment, wherein 0.70≦y≦1.8.
 4. A pigment according toclaim 3, comprising a further layer of a dielectric material having a“high” refractive index.
 5. A pigment according to claim 4, wherein thedielectric material is selected from the group consisting of siliconcarbide (SiC), zinc sulfide (ZnS), zinc oxide (ZnO), zirconium oxide(ZrO₂), titanium dioxide (TiO₂), carbon, indium oxide (In₂O₃), indiumtin oxide (ITO), tantalum pentoxide (Ta₂O₅), cerium oxide (CeO₂),yttrium oxide (Y₂O₃), europium oxide (Eu₂O₃), iron oxides such asiron(II)/iron(III) oxide (Fe₃O₄) and iron(III) oxide (Fe₂O₃), hafniumnitride (HfN), hafnium carbide (HfC), hafnium oxide (HfO₂), lanthanumoxide (La₂O₃), magnesium oxide (MgO), neodymium oxide (Nd₂O₃),praseodymium oxide (Pr₆O₁₁), samarium oxide (Sm₂O₃), antimony trioxide(Sb₂O₃), silicon monoxides (SiO), selenium trioxide (Se₂O₃), tin oxide(SnO₂), tungsten trioxide (WO₃) and combinations thereof.
 6. A pigmentaccording to claim 2 comprising in this order: (a) a silicon/siliconoxide layer obtained by heating a SiO_(y) layer in an oxygen-freeatmosphere at a temperature above 400° C., (b) a reflective layer, and(c) a silicon/silicon oxide layer obtained by heating a SiO_(y) layer inan oxygen-free atmosphere at a temperature above 400° C., wherein0.70≦y≦1.8.
 7. A pigment according to claim 2, wherein the pigmentcomprises in this order: (a2) a silicon/silicon oxide layer obtained byheating a SiO_(0.70-0.99) layer in an oxygen-free atmosphere at atemperature above 400° C., (b2) a silicon/silicon oxide layer obtainedby heating a SiO_(1.00-1.80) layer in an oxygen-free atmosphere at atemperature above 400° C., and (c2) a silicon/silicon oxide layerobtained by heating a SiO_(0.70-0.99) layer in an oxygen-free atmosphereat a temperature above 400° C., or the pigment comprises in this order:(a3) a silicon/silicon oxide layer obtained by heating a SiO_(1.00-1.80)layer in an oxygen-free atmosphere at a temperature above 400° C., (b3)a silicon/silicon oxide layer obtained by heating a SiO_(0.70-0.99)layer in an oxygen-free atmosphere at a temperature above 400° C., and(c3) a silicon/silicon oxide layer obtained by heating a SiO_(1.00-1.80)layer in an oxygen-free atmosphere at a temperature above 400° C.
 8. Apigment according to claim 2, wherein the pigment comprises in thisorder: (a4) a silicon/silicon oxide layer obtained by heating aSiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperatureabove 400° C., (b4) a silicon/silicon oxide layer obtained by heating aSiO_(1.00-1.8) layer in an oxygen-free atmosphere at a temperature above400° C., and (c4) a silicon/silicon oxide layer obtained by heating aSiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperatureabove 400° C. and optionally further layers, or the pigment comprises inthis order: (a5) a silicon/silicon oxide layer obtained by heating aSiO_(0.03-0.69) layer in an oxygen-free atmosphere at a temperatureabove 400° C., (b5) a silicon/silicon oxide layer obtained by heating aSiO_(0.70-0.99) layer in an oxygen-free atmosphere at a temperatureabove 400° C., and (c5) a silicon/silicon oxide layer obtained byheating a SiO_(0.03-0.69) layer in an oxygen-free atmosphere at atemperature above 400° C. and optionally further layers, or the pigmentcomprises in this order: (a6) a silicon/silicon oxide layer obtained byheating a SiO_(0.70-0.99) layer in an oxygen-free atmosphere at atemperature above 400° C., (b6) a silicon/silicon oxide layer obtainedby heating a SiO_(0.03-0.69) layer in an oxygen-free atmosphere at atemperature above 400° C., and (c6) a silicon/silicon oxide layerobtained by heating a SiO_(0.70-0.99) layer in an oxygen-free atmosphereat a temperature above 400° C. and optionally further layers, or thepigment comprises in this order: (a7) a silicon/silicon oxide layerobtained by heating a SiO_(100-1.80) layer in an oxygen-free atmosphereat a temperature above 400° C., (b7) a silicon/silicon oxide layerobtained by heating a SiO_(0.03-0.69) layer in an oxygen-free atmosphereat a temperature above 400° C., and (c7) a silicon/silicon oxide layerobtained by heating a SiO_(1.00-1.80) layer in an oxygen-free atmosphereat a temperature above 400° C. and optionally further layers.
 9. Acomposition comprising a high molecular weight organic material and from0.01 to 80% by weight, based on the high molecular weight organicmaterial, of a pigment according to claim
 2. 10. A cosmetic preparationor formulation comprising from 0.0001 to 90% by weight of theplane-parallel structures of silicon/silicon oxide according to claim 1and from 10 to 99.9999% of a cosmetically suitable carrier material,based on the total weight of the cosmetic preparation or formulation.11. A method for imparting color characterized by the step of adding apigment according to claim 2 to ink-jet printing materials, textiles,surface coatings, printing inks, plastics, cosmetics, glazes forceramics and glass.
 12. A method of producing plane-parallel structuresof silicon/silicon oxide, comprising the steps: a) vapour-deposition ofa separating agent onto a movable carrier to produce a separating agentlayer, b) vapour-deposition of an SiO_(y) layer onto the separatingagent layer, c) dissolution of the separating agent layer in a solvent,d) separation of the SiO_(y) from the solvent, wherein 0.70≦y≦1.8, ande) heating the SiO_(y) in an oxygen-free atmosphere to a temperatureabove 400° C.
 13. Plane-parallel structures of silicon/silicon oxideaccording to claim 1, obtained by heating plane-parallel structures ofSiO_(x) in an oxygen-free atmosphere at a temperature above 400° C.,wherein 0.05≦x≦0.50.
 14. Plane-parallel structures of silicon/siliconoxide according to claim 13, wherein 0.10≦x≦0.30.
 15. A plane-parallelpigment according to claim 2, comprising a silicon/silicon oxide layer,obtained by heating plane-parallel structures of SiO_(x) in anoxygen-free atmosphere at a temperature above 400° C., wherein0.05≦x≦0.50.
 16. A plane-parallel pigment according to claim 15, wherein0.10≦x≦0.30.
 17. A composition according to claim 9 comprising from 0.1to 30% by weight, based on the high molecular weight organic material,of a pigment according to claim
 2. 18. A pigment according to claim 5,wherein the dielectric material is selected from the group consisting ofTiO₂, ZrO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃, ZnO, a mixture of those oxides, an irontitanate, an iron oxide hydrate, a titanium suboxide and a mixture ormixed phase of those compounds.